جستجوی مقالات مرتبط با کلیدواژه "thunnus tonggol" در نشریات گروه "شیلات"

Longtail tuna (Thunnus tonggol) is an important commercial species. This species is often caught in the Oman Sea by gill net. This study was conducted to study the selectivity of longtail tuna gill net based on the length-body girth relationship from January to July 2019 monthly in Bryce, Ramin, and Konarak sampling areas. For this purpose, the caught fish were collected and the data of Longtail tuna was measured from the eye, pre-operculum, operculum, and maximum body height at each stage of sampling. Then, the net selection curve and the optimal length of the longtail tuna were calculated by the gill net selectivity model based on the net mesh size. From the results, the maximum fish length was estimated at 40, 50, 56, 65, 68, and 80 cm for the net mesh sizes of 10.1, 11.4, 13.2, 14.6, 15.2 and 17.8 cm, respectively. According to Lm50 of longtail tuna at 73.3 cm fork length, the fish caught with mesh size of 17.8 cm has a fork length greater than the average sexual maturity length of the fish. Therefore, taking into account the catch of the target species, T. tonggol, the results showed that mesh size of 10.1, 11.4, 13.2, 14.6, 15.2 cm are not suitable for catching T. tonggol in the Oman Sea. The use of 17.8 cm mesh size with the purpose of catching adult T. tonggol would be suggested for sustainable and responsible fishing for this species.

This study uses data of 5 Iranian industrial purse seiners that fish on free school tuna species in the Oman Sea. The catch data from 2015 to 2019 in the Oman Sea waters were used. The essential fish habitat of Thunnus tonggol was modeled using Satellite remote sensing (HYCOM. and MODIS). Redundancy analysis (RDA) was applied to provide a preliminary view of relationships between fish presence/absence and environmental variables, followed by the application of the Generalized Additive Model (GAM). According to GAM the presence/absence of T. tonggol is related to Latitude, Sea Surface Temperature (SST), Sea surface current velocity, and sea surface salinity (SSS). EFH maps were generated using GAM model based on the probability of the presence of T. tonggol. Latitude 23N to 25N degrees and longitude 57E to 60 E degrees are the preferred habitats of T. tonggol that are distributed in high density in these areas and indicate the habitat of this species in the continental shelf and coastal waters. Based on the analysis the distribution and density of T. tonggol on the east side of the Oman Sea Iranian waters, from Beris to Gwatar Bay, could be neglectable. Based on the results of the present study, it seems that, although, the relationship between chlorophyll-a concentration, sea surface height (SSH) and distribution, of T. tonggol is statistically significant, still the Latitude, Sea Surface Temperature (SST), Sea surface current velocity, and Sea surface salinity (SSS are the most important factors affecting the abundance of this species in the region.